Point Action cameras, as they are referred to herein, go by many other names, including point of view cameras (see, e.g., pointofviewcameras.com), helmet cameras, action cams or action cameras, point of view shooter cams, video action cameras, and extreme sports cameras among others. Brand names include GoPro. Conventional point action cameras typically have significant distortion, particularly at the outer several degrees of the field of view. In addition, astigmatism errors in conventional point action cameras can negatively impact the appearance of the video images that it captures. It is desired to have a point action camera that is capable of capturing a wide field of view, or a field of view that is greater than 90 degrees in either or both of the horizontal (x) and/or vertical (y) dimensions (or an arbitrary axis normal to the depth (z) dimension), and perhaps 135-150 degrees or more in the horizontal (x) dimension and/or perhaps 110-120 degrees or more in the vertical (y) dimension, and that is configured with built-in distortion and astigmatism correction.
Distortion in wide field of view cameras has been reduced with image processing software (see, e.g., U.S. Pat. Nos. 8,493,459 and 8,493,460, and US published patent applications nos. US20110216156 and US20110216157). It is desired however to alternatively provide a point action camera, wherein the distortion that is typically inherent in wide field of view systems such as conventional point action cameras is compensated by an effective and efficient optical design.
Alex Ning describes a six lens design in U.S. Pat. No. 7,023,628 that has a ratio of total track length (TTL) to effective focal length (EFL), or TTL/EFL, that has a maximum value of 15 over which Ning states that the design would not have been considered compact. The Ning six lens design also has a minimum value of 8 under which Ning states that the design would not achieve the required fish eye field of view. U.S. Pat. No. 7,929,221 describes multiple optical assemblies that each include three aspheric surfaces on two lens elements and that each have a TTL/EFL ratio between 15 and 25. In an unrelated technical field, U.S. Pat. No. 7,675,694 nonetheless describes multiple optical assemblies that each include six aspheric surfaces on three lens elements.
It is recognized by the present inventors that it would be advantageous to have a design with a lower TTL/EFL ratio, which takes into account the desire for compactness in physical size as well as the desire to have point action video with a wide field of view without intolerable amounts of distortion and astigmatism errors. It is desired therefore to have an optical system for a point action camera that has a low TTL/EFL ratio and that also achieves a desired wide field of view with tolerable, minimal, insubstantial, insignificant or drastically reduced distortion and astigmatism characteristics.